Prenatal Cannabis Use Linked to Preterm Birth and Birth Defects in 1.28 Million Canadian Births | Research

The takeaway

In a cohort of 1.28 million births across three Canadian provinces, prenatal cannabis use was associated with significantly increased risks of preterm birth, low birth weight, and major congenital anomalies.

Pregnant individuals, obstetric providers, public health policymakers

1.28 million births studied across 3 provinces

What the researchers found

Prenatal cannabis use (prevalence ~2%) was associated with increased risks of spontaneous preterm birth (aOR 1.80), medically indicated preterm birth (aOR 1.94), very preterm birth (aOR 1.73), low birth weight (aOR 1.90), small-for-gestational age (aOR 1.21), major congenital anomalies (aOR 1.71), cesarean section (aOR 1.13), and gestational diabetes (aOR 1.32). Female infants showed increased susceptibility for SGA and spontaneous preterm birth.

Why it matters

This is one of the largest studies ever to examine prenatal cannabis outcomes, spanning nearly 1.3 million births across multiple provinces with adjustment for important confounders including other substance use.

The numbers in context

1,280,447 births; ~2% cannabis prevalence; spontaneous preterm aOR 1.80; medically indicated preterm aOR 1.94; very preterm aOR 1.73; low birth weight aOR 1.90; congenital anomalies aOR 1.71; gestational diabetes aOR 1.32

How the study worked

Population-based retrospective cohort of 1,280,447 singleton births from three Canadian provincial registries (British Columbia, Ontario, Newfoundland/Labrador) from April 2012 to March 2019. Logistic regression adjusted for other substance use, sociodemographic factors, and comorbidities.

What this study cannot tell us

Cannabis use may be underreported. Cannot distinguish frequency, quantity, or method of cannabis use. Residual confounding possible despite statistical adjustment.

How to read the evidence

Very large population-based cohort across multiple provinces with adjustment for key confounders. One of the largest prenatal cannabis studies to date.

When this study was published

Published in 2022

The bigger picture

With cannabis legalization in Canada, this massive cohort provides some of the strongest population-level evidence that prenatal cannabis use carries meaningful risks for multiple birth outcomes.

Questions still open

Why do female infants show greater susceptibility to some cannabis-related outcomes? Does the timing of cannabis use during pregnancy (first vs third trimester) affect risk differently?

Common questions

How much does prenatal cannabis increase preterm birth risk?

This study found prenatal cannabis use nearly doubled the risk of spontaneous preterm birth (aOR 1.80) and medically indicated preterm birth (aOR 1.94) in a cohort of 1.28 million Canadian births.

Does prenatal cannabis cause birth defects?

The study found a 71% increased risk of major congenital anomalies (aOR 1.71) associated with prenatal cannabis use, though the observational design means it cannot definitively prove causation.

Read the original research

Cannabis use in pregnancy and maternal and infant outcomes: A Canadian cross-jurisdictional population-based cohort study.

PloS one, 17(11), e0276824

View on PubMed ↗Publisher’s paper ↗

Citation

Luke, Sabrina; Hobbs, Amy J; Smith, Michaela; Riddell, Catherine; Murphy, Phil; Agborsangaya, Calypse; Cantin, Christina; Fahey, John; Der, Kenny; Pederson, Ann; Nelson, Chantal. (2022). Cannabis use in pregnancy and maternal and infant outcomes: A Canadian cross-jurisdictional population-based cohort study.. PloS one, 17(11), e0276824. https://doi.org/10.1371/journal.pone.0276824